Recombinant Campylobacter jejuni subsp. jejuni serotype O:23/36 ATP synthase subunit a (atpB)

What is the role of ATP synthase subunit a (atpB) in Campylobacter jejuni metabolism?

ATP synthase subunit a (atpB) is a critical component of the F₀F₁-ATP synthase complex, which is essential for cellular energy production in C. jejuni. As part of this complex, atpB forms the membrane-embedded proton channel that allows protons to flow down their electrochemical gradient, driving the synthesis of ATP. While not explicitly mentioned in the search results, this function can be inferred from the general understanding of bacterial metabolism and the importance of energy production for pathogenic processes, including host cell entry and survival as identified in mutagenesis screens . The protein likely contributes to the bacterium's ability to adapt to different environments during infection, similar to how other metabolic genes (such as aspA and aspB) have been shown to be crucial for C. jejuni's interaction with host cells .

How does serotype O:23/36 of C. jejuni differ from other common serotypes in terms of atpB structure and function?

While the search results don't specifically address differences between serotypes regarding atpB structure, C. jejuni is known to exhibit extensive variability across serotypes, affecting various cellular components. Serotype O:23/36 may possess unique structural features in its atpB protein that could influence energy metabolism efficiency or adaptation to specific environmental conditions. Similar to how C. jejuni employs extensive O- and N-glycosylation to adapt to environmental conditions , variations in atpB across serotypes might contribute to differences in pathogenicity, host adaptation, or survival capabilities. Researchers investigating this question would need to perform comparative structural and functional analyses across different serotypes, examining amino acid sequence variations and their impact on protein function.

What expression systems are most suitable for producing recombinant C. jejuni atpB protein?

• Codon optimization: C. jejuni has a different codon usage preference than E. coli, requiring codon optimization of the atpB gene for efficient expression.

• Membrane protein challenges: Since atpB is a membrane protein component, specialized expression systems that facilitate proper membrane protein folding, such as those including membrane-targeting sequences or solubility tags, may be necessary.

• Purification strategy: Expression constructs should incorporate affinity tags (His-tag, GST, etc.) to facilitate purification, while considering how these tags might affect protein structure and function.

The expression of integral membrane proteins like atpB often requires careful optimization of induction conditions, including temperature, inducer concentration, and duration to maximize yields while minimizing toxicity to the host cells. Based on general principles for membrane protein expression, and similar to approaches used in other bacterial studies, systems that allow for controlled, slower expression would likely yield better results for functional protein production.

How does the mutation or deletion of atpB affect C. jejuni's ability to enter and survive within host epithelial cells?

While the search results don't specifically mention atpB knockout studies, they provide relevant context for understanding how such a study might be designed and interpreted. Mutagenesis screening has successfully identified genes crucial for C. jejuni's host cell entry and survival, including aspA, aspB, and sodB . A similar approach could be applied to investigate atpB.

ATP synthase function is essential for bacterial energy production, and disruption of atpB would likely have profound effects on C. jejuni's cellular energetics. This could potentially impact:

• Motility: C. jejuni depends on chemotactically controlled motility for targeted navigation to intestinal mucus and subsequent colonization . Since flagellar movement requires substantial energy, atpB disruption might severely compromise this critical virulence determinant.

• Invasion mechanisms: C. jejuni employs various energy-dependent processes for host cell invasion, including secretion of invasion antigens and inducing membrane ruffling . Disruption of energy production via atpB mutation could impair these processes.

• Intracellular survival: Following invasion, C. jejuni persists within Campylobacter-containing vacuoles, avoiding fusion with lysosomes . The maintenance of these protective compartments likely requires energy, which would be compromised in atpB mutants.

Comparative invasion assays between wild-type and atpB mutant strains, using various cell types and under different conditions, would provide valuable insights into the specific roles of this protein in pathogenesis.

What is the relationship between atpB function and C. jejuni's adaptation to microaerobic conditions?

As an obligate microaerophile, C. jejuni has evolved specialized metabolic adaptations to survive in low-oxygen environments. ATP synthase function, including the role of atpB, likely plays a critical role in this adaptation. While not directly addressed in the search results, we can infer that:

The proton motive force, which is utilized by ATP synthase for ATP production, might be regulated differently under microaerobic conditions compared to aerobic growth. The atpB subunit, forming part of the proton channel, could have specific structural or functional features that optimize energy production under microaerobic conditions.

In experimental design, researchers should consider:

• Comparative analysis: Examining atpB structure and function in C. jejuni versus aerobic bacteria could reveal adaptations specific to microaerobic metabolism.

• Oxygen gradient studies: Testing how atpB expression and ATP synthase activity change across various oxygen concentrations could provide insights into regulatory mechanisms.

• Mutational analysis: Creating specific point mutations in conserved versus variable regions of atpB and assessing their impact on growth under different oxygen levels could identify critical residues for microaerobic adaptation.

This research approach would contribute to understanding C. jejuni's fundamental metabolic adaptations that enable its unique ecological niche in the gut environment.

How does the incorporation of atpB into Campylobacter-containing vacuoles contribute to intracellular survival?

C. jejuni can persist within host cells for up to 72 hours in Campylobacter-containing vacuoles (CCVs) that avoid fusion with lysosomes . The potential role of atpB in this process represents an intriguing research question.

ATP synthase components, including atpB, might be incorporated into the membrane of CCVs, potentially contributing to:

• Maintenance of vacuolar pH: ATP synthase function could regulate the proton concentration within CCVs, creating conditions unfavorable for lysosomal degradation but optimal for bacterial survival.

• Energy provision for active processes: The bacterium may require energy for active secretion of factors that modify the vacuolar environment or interfere with host cellular processes.

• Signaling pathway modulation: CCVs enter the perinuclear space via dynein, inducing specific signaling pathways . ATP synthase activity might be involved in generating the energy required for these processes or directly participating in signaling.

To investigate this hypothesis, researchers could use immunofluorescence microscopy with antibodies against atpB to track its localization during intracellular infection, alongside markers for different host cell compartments. Complementary approaches could include live cell imaging with fluorescently tagged atpB to observe dynamics during infection, and biochemical analysis of isolated CCVs to confirm protein incorporation and functional activity.

What are the most effective protocols for purifying functionally active recombinant atpB protein while maintaining its native conformation?

Purifying membrane proteins like atpB presents significant challenges due to their hydrophobicity and tendency to aggregate. Based on general principles of membrane protein biochemistry, an effective purification protocol would likely include:

• Membrane solubilization: Careful selection of detergents is crucial. Mild detergents like n-dodecyl-β-D-maltoside (DDM) or digitonin often preserve membrane protein structure better than harsh detergents like SDS.

• Affinity chromatography: Using His-tagged constructs allows for efficient purification via nickel affinity chromatography. The protocol should include optimization of imidazole concentrations to minimize non-specific binding while maximizing target protein yield.

• Size exclusion chromatography: This additional purification step helps separate properly folded protein from aggregates and provides information about the oligomeric state.

• Functional verification: ATP synthase activity assays should be performed to confirm that the purified atpB retains its native function, potentially measuring proton translocation capability using pH-sensitive fluorescent dyes or reconstituted proteoliposome systems.

• Structural integrity assessment: Circular dichroism spectroscopy can verify secondary structure composition, while thermal stability assays can evaluate protein folding status.

Throughout the purification process, it's essential to maintain appropriate buffer conditions (pH, ionic strength) and consider adding stabilizing agents such as glycerol or specific lipids that might be required for proper atpB function.

How can researchers effectively measure the contribution of atpB to ATP synthesis in C. jejuni under different environmental conditions?

To accurately assess atpB's contribution to ATP synthesis under various conditions relevant to C. jejuni's lifecycle, researchers should consider a multi-faceted approach:

• In vitro ATP synthesis assays: Using purified ATP synthase complexes (wild-type and atpB variants) reconstituted into liposomes to measure ATP production rates under controlled proton gradients.

• Whole-cell bioenergetic analysis: Employing techniques like the Seahorse XF Analyzer to measure oxygen consumption rates and extracellular acidification in intact bacteria under different conditions (varying oxygen levels, pH, temperature).

• Membrane potential measurements: Using fluorescent probes like DiSC3(5) to measure membrane potential in wild-type versus atpB-modified strains, providing insights into proton gradient maintenance.

• Conditional expression systems: Developing strains with inducible atpB expression to allow time-course studies of how varying atpB levels affect cellular energetics.

• Environmental mimicry: Designing experimental conditions that simulate different host environments (gastric pH, intestinal conditions, intracellular compartments) to assess how atpB function adapts across the infection cycle.

What techniques are most reliable for studying interactions between atpB and other C. jejuni proteins during host cell invasion?

Understanding protein-protein interactions involving atpB during host cell invasion requires sophisticated techniques that can capture these often transient and context-dependent associations. Based on approaches used in similar research contexts, the following methods would be most appropriate:

• Co-immunoprecipitation (Co-IP): Using antibodies against atpB to pull down associated proteins during different stages of host cell invasion, followed by mass spectrometry identification. This approach would need careful optimization to preserve membrane protein complexes.

• Bacterial two-hybrid systems: Modified to accommodate membrane proteins, these systems could screen for potential interaction partners in a controlled environment.

• Proximity labeling techniques: Methods like BioID or APEX2, where atpB is fused to a promiscuous biotin ligase that biotinylates nearby proteins, allowing identification of the proximal interactome in living bacteria during infection.

• Förster Resonance Energy Transfer (FRET): Using fluorescently tagged atpB and candidate interaction partners to detect close associations in living cells during the infection process.

• Cross-linking coupled with mass spectrometry: Chemical cross-linking can capture transient interactions, which are then identified by mass spectrometry after protein digestion.

When interpreting data from these experiments, researchers should be mindful that C. jejuni utilizes complex invasion mechanisms including fibronectin binding proteins, other adhesins, and the flagellum as a type-3-secretion system . The ATP synthase components might interact with multiple cellular systems during invasion, requiring careful experimental design to distinguish direct interactions from indirect associations within larger complexes.

How should researchers interpret differences in atpB sequence variations across clinical isolates of C. jejuni?

When analyzing atpB sequence variations across clinical isolates, researchers should adopt a systematic approach that integrates sequence analysis with functional implications:

• Conservation analysis: Identify highly conserved regions likely essential for basic function versus variable regions that might relate to strain-specific adaptations. This requires alignment of atpB sequences from diverse isolates, with special attention to serotype O:23/36 characteristics.

• Structure-function correlation: Map variations onto predicted structural models of atpB to determine if changes occur in transmembrane domains, proton channel regions, or protein-protein interaction interfaces.

• Clinical correlation: Analyze whether specific sequence variations correlate with clinical outcomes, invasion efficiency, or antibiotic resistance profiles. This requires integration of sequence data with patient metadata and experimental phenotyping.

• Evolutionary context: Apply population genetics approaches to determine if variations represent neutral drift or positive selection, potentially indicating adaptive significance.

• Experimental validation: Selected variations should be introduced into reference strains via site-directed mutagenesis to directly test their functional impact on ATP synthesis, growth characteristics, and virulence.

When presenting this data, researchers should develop comprehensive tables showing amino acid variations across positions, with annotations for predicted functional significance, frequency across isolates, and association with specific serotypes or clinical presentations.

What computational approaches are most effective for predicting atpB structure and functional domains in C. jejuni?

Given the challenges in obtaining experimental structures for membrane proteins like atpB, computational approaches offer valuable alternatives. For C. jejuni atpB structural prediction, researchers should consider:

• Homology modeling: Using experimentally determined structures of ATP synthase subunit a from other organisms as templates. While sequence identity might be moderate, the fundamental architecture of ATP synthase components is often conserved across species.

• Deep learning approaches: Recent advances in protein structure prediction, particularly AlphaFold2 and RoseTTAFold, have dramatically improved accuracy for membrane proteins and should be applied to atpB analysis.

• Molecular dynamics simulations: To refine structural models and assess stability in a membrane environment, especially focusing on proton channel residues.

• Coevolutionary analysis: Methods like Direct Coupling Analysis can identify residue pairs that have co-evolved, providing insights into structural contacts and functional domains.

• Integrative approaches: Combining computational predictions with limited experimental data (such as cysteine accessibility, cross-linking, or EPR spectroscopy results) to constrain and validate models.

Functional domain prediction should focus on identifying:

• Transmembrane helices and their orientation

• Proton-conducting channel residues

• Interaction surfaces with other ATP synthase components

• Potential regulatory sites

The resulting structural models can guide hypothesis generation for experimental studies, particularly for designing site-directed mutagenesis to probe structure-function relationships.

What controls are essential when investigating the role of atpB in C. jejuni pathogenesis using cell culture models?

Robust experimental design for investigating atpB's role in pathogenesis requires carefully selected controls to ensure valid interpretations. Essential controls include:

By incorporating these controls, researchers can confidently attribute observed phenotypes to atpB function and distinguish between direct effects on pathogenesis versus indirect consequences of altered energy metabolism.

How can researchers effectively combine in vitro and in vivo approaches to comprehensively understand atpB's role in C. jejuni infection?

A comprehensive understanding of atpB's role requires integrating evidence across multiple experimental systems. An effective research strategy would include:

• Sequential experimental pipeline:

  • Initial characterization in simplified in vitro systems (purified proteins, membrane vesicles)

  • Progression to cell culture models (adhesion, invasion, survival assays)

  • Validation in animal infection models (e.g., mouse or chicken colonization models)

• Parallel phenotyping approach:

  • Simultaneously assess multiple aspects of C. jejuni physiology and virulence (motility, stress resistance, adhesion, invasion, intracellular survival) to develop a comprehensive phenotypic profile for atpB mutants

• Translational correlation studies:

  • Compare findings from laboratory strains with clinical isolates

  • Assess atpB expression in samples obtained directly from infected hosts

  • Correlate atpB sequence variations with clinical outcomes

• Mechanistic dissection:

  • Use in vitro systems to precisely characterize biochemical functions

  • Apply findings to interpret more complex phenotypes observed in vivo

  • Develop testable hypotheses that bridge molecular mechanisms and infection outcomes

These approaches should be tailored to address specific aspects of C. jejuni pathogenesis, particularly its ability to enter and survive within host cells, which has been identified as crucial for colonization in animal models . The experimental design should also consider the multiple virulence factors and adaptation mechanisms employed by C. jejuni, including its use of proteases to open cell-cell junctions and its ability to avoid lysosomal fusion .

What are the most promising research directions for understanding how atpB contributes to antibiotic resistance in C. jejuni?

While ATP synthase is not traditionally considered an antibiotic resistance determinant, emerging evidence suggests potential links between energy metabolism and antimicrobial susceptibility. For C. jejuni atpB research, promising directions include:

• Macrolide interaction studies: Given the information about macrolide antibiotics and their distribution in tissues , researchers should investigate whether ATP synthase activity affects the accumulation or efficacy of macrolides in C. jejuni. This is particularly relevant since macrolides like azithromycin achieve high concentrations in lung tissue and pulmonary epithelial lining fluid compared to plasma , which might have parallels in intestinal tissues relevant to C. jejuni infection.

• Membrane potential and antibiotic uptake: Since many antibiotics require either membrane potential or ATP for uptake, alterations in atpB function might indirectly contribute to resistance by reducing antibiotic accumulation within bacterial cells.

• Stress response coordination: ATP synthase function might be linked to stress response mechanisms that contribute to antibiotic tolerance, particularly in response to membrane-targeting antibiotics.

• Persister cell formation: Investigate whether modulation of ATP synthase activity contributes to persister cell formation in C. jejuni, potentially explaining the recalcitrance of some infections to antibiotic treatment.

• Combination therapy targets: Explore whether compounds targeting ATP synthase could sensitize C. jejuni to existing antibiotics, potentially revitalizing the efficacy of treatments to which resistance has emerged.

These research directions could lead to novel therapeutic approaches that target energy metabolism as an adjunct to conventional antibiotic therapy, addressing the growing concern of antimicrobial resistance in Campylobacter species.

How might atpB function interact with other virulence determinants during different stages of C. jejuni infection?

The complex pathogenesis of C. jejuni likely involves coordinated action between multiple virulence systems, with energy metabolism playing a supporting but crucial role. Future research should explore:

• Temporal regulation analysis: Investigating how atpB expression and ATP synthase activity change during different infection stages (initial colonization, epithelial cell invasion, intracellular survival).

• Virulence factor secretion dependence: Determining whether energy provided by ATP synthase is differentially required for various secretion systems, particularly the flagellar type III secretion system used by C. jejuni .

• Co-regulation networks: Exploring potential regulatory links between atpB and established virulence factors, including adhesins like CadF and FlpA , through transcriptomic and proteomic approaches under infection-relevant conditions.

• Metabolic adaptation integration: Examining how ATP production through atpB interacts with other metabolic adaptations C. jejuni employs during infection, such as utilization of specific carbon sources in the intestinal environment.

• Host response modulation: Investigating whether ATP synthase activity affects the production of virulence factors that modulate host immune responses, such as the cytolethal distending toxin that directs cells toward programmed death .